Abstracts for the 6th International GAME Conf.
3-5 December 2004
Kyoto Japan
Impact of rooting depth on transpiration over a hill evergreen forest in northern Thailand
Katsunori Tanaka, Hideki Takizawa, Tomonori Kume, Jianqing Xu, Chatchai Tantasirin, and Masakazu Suzuki (1)
(1) Frontier Research Center for Global Change, Nihon University, University of Tokyo, Frontier Research Center for Global Change, Kasetsart University, and University of Tokyo
Possible impacts of rooting depth on vegetative processes have also been discussed because rooting depth limits soilwater use. Previous research showed that transpiration in an evergreen broad-leaved forest in northern Thailand (18o48f N, 98o54f E) peaked at the end of the dry season. However, rooting-depth limitations on soilwater use were not investigated. This study examined the impact of rooting depth and soil hydraulic properties on transpiration using a newly developed soil plant air continuum (SPAC) model. The soil texture at the site was classified as silty sand from the measured relationship between the volumetric soilwater content and soilwater potential at 0.1-m depths. To effectively simulate heat-pulse velocity variation corresponding to dry-season transpiration and annual discharge, a rooting depth of 4-5 m was needed, assuming a silty sand soil texture under unsaturated conditions. This value is less than the reported maximum rooting depth of evergreen trees and is considered reasonable. A penetration test showed that soil became harder at depths of 4-5 m. The model results suggest that a shallower rooting depth is sufficient to maintain the late-dry-season transpiration peak if other soil textures with lower hydraulic conductivity are assumed. By contrast, the late-dry-season transpiration peak could not be maintained under unsaturated conditions if a sandy soil texture with high hydraulic conductivity was assumed, even with a rooting depth of 12 m.
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Frontier Research Center for Global Change | |
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3173-25 Showamachi, Kanazawa-ku, Yokohama, Kanagawa 236-0001 | |
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